This project concentrates on the structure of the ribosome at or near functional sites. Of special interest are the tRNA biding sites, regions near the ends of the ribosomal RNAs, and the sites of interaction of the antibiotics erythromycin and streptomycin. Fluorescent derivatives of ribosomal components and ligands are prepared which still maintain significant functional activity. Distances between pairs of dyes are measured by singlet energy transfer. Individual derivatives are used for kinetic and equilibrium studies of ribosome-ligand interaction. Quenching and polarization measurements allow the accessibility and flexibility of sites to be examined. Components of functional sites are identified by affinity labeling. Site-specific reaction is insured by coupling covalent modification to subsequent function. Various chemical techniques for examining the location and properties of regions of ribosomal RNAs are being examined. These include tritium exchange studies of secondary structure, antibodies against minor bases, and photochemical crosslinkers.